This invention relates to a power-limiting control method and system for a work vehicle.
Up to the present time, many work vehicles have been powered by internal combustion engines, such as diesel engines. For the future, hybrid vehicles offer promise for compliance with evolving exhaust emission regulations in the United States and other countries. A hybrid vehicle may be used for both an internal combustion engine and an electrical drive motor for propulsion. Typically, the internal combustion engine operates to generate power for operation of one or more electric drive motors. In one configuration of a hybrid vehicle, the internal combustion engine may be turned off and the vehicle may operate electrically in a quiet mode by extracting electrical energy stored in batteries. Although work vehicles could potentially be propelled electrically, solely by electrical motors and batteries, the weight of batteries and the charge capacity limits the useful range and duty cycle of such vehicles.
Fuel cells may be used to replace batteries as the primary electrical energy source of a vehicle. Fuel cells may be used to convert hydrogen into electrical energy. However, fuel cells remain expensive to manufacture, which is an obstacle to their introduction to their broad market acceptance. Even if fuel cells become commercially viable for work vehicles, the maximum range and maximum working time of the fuel-cell vehicle may be limited by the storage capacity of tanks for storing compressed gas (e.g., hydrogen). Thus, a need exists for managing power consumption to enhance the longevity of operation of electrically powered and hybrid work vehicles.
In accordance with one embodiment of the method and system of the invention, a capacity estimator determines a total maximum allowable power storage capacity for a work vehicle. A timer times the operating time of the work vehicle in an electrically propelled mode, where energy for propulsion is obtained materially, primarily or entirely from an energy storage device. A load manager, a driver or both decrease the available power to at least one of a drive motor of the work vehicle and an ancillary load over the operating time to conserve the available power stored for operating at least one critical load of the work vehicle.